In recent years, researches have been actively performed on a device for directly controlling a living organism system such as an implanted medical apparatus or a nerve stimulation electrode. However, an interface between the artificial device and the living organism system has various problems caused by a difference in constituting materials and a significant difference in the physical characteristic and the chemical characteristic. For example, when a metal electrode is used to apply an electrical stimulation to cells, the cells are undesirably damaged by the toxicity of eluted metal ions or bubbles caused by electrolyzation.
In order to reduce the problems as described above, it is important to establish an interface by such material that can provide efficient information transmission and that is highly compatible with a living organism (i.e., a bio interface). Materials compatible with a living organism include conductive polymer that is highly flexible and that has a high interfacial capacity. For example, cells can be electrically stimulated efficiently by coating a metal surface with conductive polymer compatible with a living organism.
If hard material such as metal or glass is used around cells involved in expansion and contraction such as muscle cells, the material not only limits the expansion and contraction but also causes a difficulty in the adhesion of the cells to the material due to expansion and contraction.
Due to this reason, the artificial device has been required to be composed of flexible material closer to a living organism tissue. Such material exemplarily includes hydrogel such as agarose gel, fibrin gel, or collagen gel. These hydrogels have a solid state, can retain a large amount of water, and are flexible. Thus, applications of these hydrogels for a solid electrolyte have been developed (see Patent References 1 to 3). Some hydrogels are highly compatible with a living organism and have been used for a cell culture substrate and a bioreactor for example.
Techniques to perform the electropolymerization of conductive polymer at the surface or the interior of porous material such as hydrogel includes polypyrrole electropolymerization carried out in the University of Michigan (see Nonpatent Reference 1). According to Nonpatent Reference 1, polypyrrole polymerized on an electrode covered with gel starts growing from the gel fibers in a three-dimensional manner, demonstrating an improved performance of a nerve stimulation electrode. However, in the case of Nonpatent Reference 1, the gel-covered electrode, the gel, and the conductive polymer are structured in an integrated manner, thus failing to provide an elastic electrode.
Regarding the patterning of conductive polymer, many methods have been suggested, including lithography using resist (see Patent Reference 4), a micro contact printing method (see Nonpatent Reference 2), scanning electrochemical microscopy (see Nonpatent Reference 3), photochemical reaction method (see Nonpatent Reference 4), screen printing (see Nonpatent Reference 5), ink jet printing (see Patent Reference 5 and Nonpatent Reference 6), a capillary method (see Nonpatent Reference 7), a transfer method (see Nonpatent Reference 8), and a clip pen method (see Nonpatent Reference 9). All of these techniques perform patterning of conductive polymer on a rigid substrate such as glass and thus cannot be used for aqueous porous material such as gel.
The material that is aqueous porous material such as gel and that is porous material including electrolyte includes gel material such as agarose gel or fibrin gel. Such electrolyte gel is highly aqueous. Thus, in the case of an existing known technique such as a dispersion liquid coating by an inkjet printer, it is difficult to realize the pattern printing of such material.